High performance fabrics have been used for numerous applications where tear-resistance, abrasion-resistance, cut- and stab-resistance, and chemical- and cold-resistance are important. As used herein, the term “high performance” refers to fabrics constructed from a group of fibers used to make cut-resistant and abrasion resistant articles such as cable and rope covers, hovercraft curtains, gun and boat covers, gloves, and aprons. The high strength-to-weight ratios of these fabrics can provide properties having significant improvements in the performance characteristics stated above at a fraction of the weight of other alternatives.
It has been found desirable to combine the advantages of high performance fabrics with thermoplastic film laminates for applications where the fabric also must be air and water impervious. Fabrics for such applications were previously typically constructed from vinyl-coated nylon or similar materials which do not exhibit high performance characteristics.
Recently, a thermoplastic film such as EVA has been bonded to a substrate of high performance fabric to create a more durable, cut and wear resistant flexible laminate that is also air and water impermeable. This high performance fabric is preferably constructed from an extended chain polyethylene such as ultra high molecular weight polyethylene. EVA provides a superior bond to the ultra high molecular weight polyethylene fabric; however, it has been found by the inventors that an EVA laminate becomes soft and tacky when exposed to temperatures above about 120 degrees Fahrenheit. As used herein, “tacky” refers to the property of a material wherein it is sticky and lacks a smooth, slick surface over which objects may slide with minimal friction. As will be appreciated by those skilled in the materials arts, when a film becomes soft and tacky, it is not only susceptible to degradation, but also to damage caused by objects that may impinge or otherwise impact the film. For example, a film subject to such degradation would prove highly unsuitable in warm or hot environments that are subject to severe weather such as tropical storms or hurricanes. Further, the tacky condition will degrade any operation in which objects must move over or make contact with the film; e.g., a conveyor belt. While it has been found that both low and high density polyethylene may be subjected to such elevated temperatures without becoming soft or tacky, the inventors have also found that polyethylene does not provide the degree of bonding to certain high performance fabrics, such as high molecular weight polyethylene fabrics, needed for certain applications. Thus, each of the two types of thermoplastic film provides at least one superior physical property over the other.
The inventors therefore have discovered a need then for a process that securely and reliably bonds a thermoplastic film to a high molecular weight polyethylene fabric and that has an outer film surface that will not degrade, become tacky, or soft under anticipated operational conditions.